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rust-bors merged 1 commit into from
May 5, 2026
+90 −28
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Print HRTB binders before fn qualifiers #156058

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55 changes: 30 additions & 25 deletions compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -779,49 +779,54 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
let (lt1, sig1) = get_lifetimes(sig1);
let (lt2, sig2) = get_lifetimes(sig2);

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
let mut values =
(DiagStyledString::normal("".to_string()), DiagStyledString::normal("".to_string()));

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^^^^
let safety = |fn_def, sig: ty::FnSig<'_>| match fn_def {
None => sig.safety().prefix_str(),
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^^^^^^^^^^^^^^
let fn_item_prefix_and_safety = |fn_def, sig: ty::FnSig<'_>| match fn_def {
None => ("", sig.safety().prefix_str()),
Some((did, _)) => {
if self.tcx.codegen_fn_attrs(did).safe_target_features {
"#[target_features] "
("#[target_features] ", "")
} else {
sig.safety().prefix_str()
("", sig.safety().prefix_str())
}
}
};
let safety1 = safety(fn_def1, sig1);
let safety2 = safety(fn_def2, sig2);
let (prefix1, safety1) = fn_item_prefix_and_safety(fn_def1, sig1);
let (prefix2, safety2) = fn_item_prefix_and_safety(fn_def2, sig2);
values.0.push(prefix1, prefix1 != prefix2);
values.1.push(prefix2, prefix1 != prefix2);

// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^^^^
let lifetime_diff = lt1 != lt2;
values.0.push(lt1, lifetime_diff);
values.1.push(lt2, lifetime_diff);

// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^^
values.0.push(safety1, safety1 != safety2);
values.1.push(safety2, safety1 != safety2);

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^^^^^^^^
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^^^^^^
if sig1.abi() != ExternAbi::Rust {
values.0.push(format!("extern {} ", sig1.abi()), sig1.abi() != sig2.abi());
}
if sig2.abi() != ExternAbi::Rust {
values.1.push(format!("extern {} ", sig2.abi()), sig1.abi() != sig2.abi());
}

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^^^^^^
let lifetime_diff = lt1 != lt2;
values.0.push(lt1, lifetime_diff);
values.1.push(lt2, lifetime_diff);

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^
values.0.push_normal("fn(");
values.1.push_normal("fn(");

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^^^
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^
let len1 = sig1.inputs().len();
let len2 = sig2.inputs().len();
if len1 == len2 {
Expand Down Expand Up @@ -859,13 +864,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
values.1.push("...", !sig1.c_variadic());
}

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^
values.0.push_normal(")");
values.1.push_normal(")");

// unsafe extern "C" for<'a> fn(&'a T) -> &'a T
// ^^^^^^^^
// #[target_features] for<'a> unsafe extern "C" fn(&'a T) -> &'a T
// ^^^^^^^^
let output1 = sig1.output();
let output2 = sig2.output();
let (x1, x2) = self.cmp(output1, output2);
Expand Down
12 changes: 12 additions & 0 deletions tests/ui/mismatched_types/fn-pointer-mismatch-diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,19 @@ fn foo(x: i32) -> u32 {
0
}

extern "C" fn extern_foo(_: &i32) {}

unsafe extern "C" fn unsafe_extern_foo(_: &i32) {}

fn rust_foo(_: &i32) {}

fn main() {
let b: fn() -> u32 = bar; //~ ERROR mismatched types [E0308]
let f: fn(i32) = foo; //~ ERROR mismatched types [E0308]

// See https://github.com/rust-lang/rust/issues/151393
let _: for<'a> fn(&'a i32) = extern_foo; //~ ERROR mismatched types [E0308]
let _: for<'a> fn(&'a i32) = unsafe_extern_foo; //~ ERROR mismatched types [E0308]
let _: for<'a> extern "C" fn(&'a i32) = rust_foo; //~ ERROR mismatched types [E0308]
let _: for<'a> unsafe extern "C" fn(&'a i32) = rust_foo; //~ ERROR mismatched types [E0308]
}
51 changes: 48 additions & 3 deletions tests/ui/mismatched_types/fn-pointer-mismatch-diagnostics.stderr
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:14:26
--> $DIR/fn-pointer-mismatch-diagnostics.rs:20:26
|
LL | let b: fn() -> u32 = bar;
| ----------- ^^^ expected fn pointer, found fn item
Expand All @@ -10,7 +10,7 @@ LL | let b: fn() -> u32 = bar;
found fn item `fn() -> () {bar}`

error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:15:22
--> $DIR/fn-pointer-mismatch-diagnostics.rs:21:22
|
LL | let f: fn(i32) = foo;
| ------- ^^^ expected fn pointer, found fn item
Expand All @@ -20,6 +20,51 @@ LL | let f: fn(i32) = foo;
= note: expected fn pointer `fn(_) -> ()`
found fn item `fn(_) -> u32 {foo}`

error: aborting due to 2 previous errors
error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:24:34
|
LL | let _: for<'a> fn(&'a i32) = extern_foo;
| ------------------- ^^^^^^^^^^ expected "Rust" fn, found "C" fn
| |
| expected due to this
|
= note: expected fn pointer `for<'a> fn(&'a _)`
found fn item `for<'a> extern "C" fn(&'a _) {extern_foo}`

error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:25:34
|
LL | let _: for<'a> fn(&'a i32) = unsafe_extern_foo;
| ------------------- ^^^^^^^^^^^^^^^^^ expected safe fn, found unsafe fn
| |
| expected due to this
|
= note: expected fn pointer `for<'a> fn(&'a _)`
found fn item `for<'a> unsafe extern "C" fn(&'a _) {unsafe_extern_foo}`
= note: unsafe functions cannot be coerced into safe function pointers

error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:26:45
|
LL | let _: for<'a> extern "C" fn(&'a i32) = rust_foo;
| ------------------------------ ^^^^^^^^ expected "C" fn, found "Rust" fn
| |
| expected due to this
|
= note: expected fn pointer `for<'a> extern "C" fn(&'a _)`
found fn item `for<'a> fn(&'a _) {rust_foo}`

error[E0308]: mismatched types
--> $DIR/fn-pointer-mismatch-diagnostics.rs:27:52
|
LL | let _: for<'a> unsafe extern "C" fn(&'a i32) = rust_foo;
| ------------------------------------- ^^^^^^^^ expected "C" fn, found "Rust" fn
| |
| expected due to this
|
= note: expected fn pointer `for<'a> unsafe extern "C" fn(&'a _)`
found fn item `for<'a> fn(&'a _) {rust_foo}`

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0308`.
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